1. Field of the Invention
An aspect of the present invention relates to an image forming apparatus and a communication method with trays thereof; and, more particularly, to an image forming apparatus that can communicate with trays through a single communication channel and assign an identification (ID) to each tray simply and accurately, and its communication method with its trays.
2. Description of the Related Art
Recently, functions of image forming apparatuses are diversified such as a function of a printer and a function of a copier, and the image forming apparatuses are connected through a network. This has increased the required quantity of recording media and thus the image forming apparatuses should be equipped with many optional trays. Therefore, image forming apparatuses with a plurality of optional trays stacked in multiple steps are widely used these days. Each optional tray of an image forming apparatus communicates with the main body of the image forming apparatus through a communication channel. Herein, a one-to-one communication UART is usually used as the communication scheme.
FIG. 1 is a schematic diagram showing a conventional communication scheme between the main body of an image forming apparatus and its optional trays. According to the UART communication scheme shown in the drawing, the main body 10 of the image forming apparatus is assigned in advance with as many communication channels as the number of available optional trays 20, 30 and 40 and, when each optional tray 20, 30 or 40 is mounted in the main body 10, it is connected to the main body 10 to be able to communicate through a one-to-one communication channel. Therefore, since the main body 10 uses a separate communication channel to communicate with each optional tray 20, 30 or 40 one-to-one, it requires as many communication channels as the number of optional trays 20, 30 and 40.
A first optional tray 20 is connected to the main body 10 through a first UART communication channel, and a second optional tray 30 is connected to the main body 10 through a second UART communication channel. Likewise, a third optional tray 40 is connected to the main body 10 through a third UART communication channel. Thus, the image forming apparatus transmits a control command through the first UART to operate the first optional tray 20 and transmits a control command through the second UART to operate the second optional tray 30. For example, when the main body 10 transmits a feeding command to the second optional tray 30 through the second UART, the second optional tray 30 drives a feeding motor for operating a feeding roller (not shown) to feed a recording medium.
Since the conventional image forming apparatus performs one-to-one communication between its main body 10 and each optional tray 20, 30 or 40 through a UART communication channel, it has an advantage that communication protocol is simple. However, it requires as many communication channels as the number of optional trays it can have in the main body 10 and it takes a high amount of costs to form the main body 10 to be connected with a plurality of communication channels. Moreover, since many communication channels are applied to the main body 10, the conventional image forming apparatus has a shortcoming that a Central Processing Unit (CPU) of the main body 10 suffers much load.
In order to reduce the amount of load applied to the CPU, a method of connecting the main body and optional trays through a UART communication channel and then connecting a first optional tray and a second optional tray through a UART communication channel has been suggested. However, although the method can reduce the amount of load applied to the CPU, it still requires as many UART communication channels as the number of optional trays because it needs a UART communication channel between the main body and the first optional tray and a UART communication channel between the first optional tray and the second optional tray separately. Therefore, there are problems that it takes much cost for building up a plurality of UART communication channels and that the circuit is complex.
Since the conventional image forming apparatus needs as many UART communication channels as optional trays, the number of optional trays that can be used in the image forming apparatus is limited.
To solve the problem, a method that can reduce costs and complexity in the circuit by using a single communication channel between the main body and the optional trays should be sought.
Korean Patent No. 10-378172 entitled “Tray recognizing apparatus and method,” discloses a structure where each of a plurality of optional trays is assigned an ID. According to this technology, a power supplier of the main body supplies power to a controller of a first optional tray, and the first optional tray transmits the power to a second optional tray. In short, the power is supplied from the main body to the optional trays sequentially. Herein, since each optional tray has a resistance set up therein, the level of power is decreased as the power passes through each resistance. Thus, the main body can assign an ID to each optional tray based on the voltage value of power applied to each optional tray. However, since a contact resistance may be generated by a connector, the voltage value applied to each optional tray can be different from an expected level and the voltage difference between the optional trays can be diverse. Therefore, an error may occur when the main body communicates with each optional tray or when an ID is assigned to each optional tray.
Other than the above-described method, there is a method of providing a switch for manually setting each optional tray. According to this method, a user turns on a switch after mounting each optional tray. Then, each optional tray recognizes its own ID and transmits its ID to a main controller. This method, however, has a drawback in that a user has to manually manipulate the switch and, if the same ID is set for a different optional tray due to a mistake of the user, data can be entangled during data transmission and reception.
Therefore, a method that can relieve users from manually setting up an ID and assigning an ID to each optional tray rapidly and accurately is needed.